If you measured the headlight voltages at the headlights themselves (both power and ground wires) then the ground path question isn't relevant but if you measured from the lamp power wire to somewhere on the chassis (a bolt etc.) then it's very relevant.
The left xenon headlight is connected to ground (earth, chassis, -ve, etc.) at earth junction X165.
in front left wheelhouse
The right xenon headlight is connected to ground (earth, chassis, -ve, etc.) at earth junction X166 and X1106.
wheel well, front right
If you have fully adaptive xenon lighting (turn left and right as well as up and down) there is an additional ground point for both lights at X10012.
footwell, passenger's side LH A-pillar
Check all the brown wires are secure and that the ground terminal is well connected to the bodywork. You might even want to do a resistance test from each ground junction back to the large ground terminal on the inside of the left front fender (the used for jump starting). Should be a very low resistance.
HTH...